Electrochemical and Electrogenerated Chemiluminescent Studies of a Trinuclear Complex, [((phen)2Ru(dpp))2RhCl2]5+, and Its Interactions with Calf Thymus DNA

The electrochemical behavior of a trinuclear ruthenium(H)containing complex, [((phen)(2)Ru(dpP))(2)RhCl2](5+) (where phen = 1,10-phenanthroline, dpp = 2,3-bis(2-pyridyl)pyrazine), was studied in acetonitrile (MeCN) and aqueous solutions. In MeCN containing 0.10 M tetran-butylammonium perchlorate (TBAP), the complex displayed a reversible, overlapping Ru-II/III redox process with E-1/2 = +1.21 V vs Ag/Ag+ (10 mM), an irreversible reduction of Rh-III/I at -0.73 V vs Ag/Ag+, and two quasi-reversible dpp/dpp(-) couples with E1/2 = -1.11 and -1.36 V vs Ag/Ag+ at a Pt electrode with a scan rate of 50 mV s(-1). In 0.20 M Tris buffer solution (pH 7.4), an irreversible, overlapping Ru-II/III oxidation at +1.48 V vs Ag/AgCl (3 M KCl), and an irreversible reduction of Rh-III/II at -0.78 V vs Ag/AgCl were observed at a glassy carbon electrode with a scan rate of 50 mV/s. Investigations on the electrogenerated chemiluminescence (ECL) of the complex revealed that 2-(dibutylamino) ethanol (DBAE) was superior to tri-n-propylamine (TPrA) as an ECL coreactant within their entire concentration range of 10-100 mM in MeCN, and in aqueous media, as low as 1.0 nM of the complex can be detected using TPrA coreactant ECL. A maximum ECL emission of 640 nm, which is about 55 run blue shift to its fluorescence, was observed in MeCN with DBAE as a coreactant. Interactions of the complex with calf thymus DNA (ctDNA) were conducted with a flow-cell based quartz-crystal microbalance, and a binding constant of 2.5 x 10(5) M-1 was calculated on the basis of the Langmuir isotherm equation.